Patent GB-1081593-A (GB)
Title: Improvements in or relating to telecommunications systems
IPC: H04Q3/00
Filed: 1965-12-06
Abstract: 1,081,593. Automatic exchange systems. SIEMENS A.G. Dec. 6, 1965 [Dec. 5, 1964], No. 61603/65. Heading H4K. An exchange uses a path finding network which combines selection of a path between a calling subscriber and an outgoing junction in the local network with selection of a preferred inter-exchange route from the alternatives available. The exchange network considered is shown in Fig. 1 and the corresponding interexchange route selection network for exchange 71 is shown in Fig. 3a in which f71-g71 represents the path seeking network for the switches of exchange 71. Path seeking in the network f71-g71 is of the kind described in Specifications 944,736 or 897,677. For each exchange in the network other than 71 a gate such as K331, K715, is provided, application of the wanted exchange code to one out of each of the three groups of ten marking leads N1, N2, N3, causing the corresponding exchange gate to conduct and extend the marking to terminals in the route selecting network such as Z331, Z715. Corresponding coincidence gates f331 to f715 are provided for each exchange in the system and the terminals Z331 to Z715 are connected to the right-hand terminals of their corresponding gates and to the right-hand terminals of such gates as correspond to exchanges over which alternative routes may be set up. Thus exchange 331 is accessible to exchange 71 direct, by way of exchange 33, or by way of exchanges 3 and 33 in tandem. Terminal Z331 is therefore connected to gates f331, f33 and f3. If a path is to be available over exchanges 7, 3, and 33, in tandem Z331 would also be connected to gate f7 as shown in dotted line. The left-hand terminals of the gates f331 to f715 are connected to terminals fD1 to fDm of the path seeking network of exchange 71. Each such terminal corresponds to a switch in the stage giving access to outgoing junctions in exchange 71 and, as shown, each such switch provides only one path to each distant exchange. Outgoing paths available to a calling subscriber are indicated by network f71-g71 which extends marks from terminals fD1 to fDm to the lefthand side of gates f331 to f715, the busy or idle state of the outlet being indicated by contacts 1a1 being open or closed in the connections. If the wanted distant exchange is 331 a mark is applied to the right-hand side of gate 331 from gate K331 which also marks the right-hand side of gates f 33 and f3 to indicate alternative routes. If all routes are available gates f331, f 33 and f3 extend marks to a preferred route selector LW which in the present instance selects the output of gatef331 (the right-hand gate of the active set) and relays the mark to terminal g331. The terminals g331 to g715 are connected to coincidence gates Ud1 to Udm which comparison the terminals fD1 to fDm. The terminals g331 to g715 therefore indicate the primary route to be taken from the exchange and marking a set of the gates Ud1 to Udm indicate which outgoing switches in exchange 71 are involved. The markings on terminals fD1 to fDm provide a second input to gates Ud1 to Udm to indicate which of the switches so indicated are available. Contacts 2a1 disconnect those markings to switches which are busy on the wanted route. The network f71- g71 selects one of these available outlets and thereby determines the route. If no direct route is'available to exchange 331 the left-hand terminal of gate f 331 receives no input and circuit LW will consider second choice routes by way of exchange 33 as indicated by gate f 33. If routes between exchanges 33 and 331 are blocked a contact in the connection between terminal Z331 and gate f33 opens to inhibit gate f 33. Where f 33 gives no output, third choice routes as indicated by gate f 3 are considered by LW. If, however, routes between exchanges 3 and 33 or 33 and 331 are blocked, contacts in the connection between terminal Z331 and gate f3 open to inhibit gate f3. Each outgoing switch in exchange 71, corresponding totheterminals fD1 to fDm and associated gates Ud1 to Udm, may provide more than one outlet to each distant exchange so long as selecting network f71-g71 contains means to select one of them when more than one is available. The circuit LW chooses the right-hand output of gates f331 to f715 but may in other cases select the left-hand output, the circuit LW being conditioned one way or the other according to the exchange code as made available to terminals p3, p7. Instead of marking the terminals Z331, Z33, and Z3, at the same time and effecting selection of the preferred route in circuit LW; the terminals may be marked one after the other in order of preference, the sequence being halted as soon as a route is determined (Figs. 4a and 4b, not shown). Circuitry to apply such sequential marking must, to some extent at least, be peculiar to each exchange code. The arrangement described differs also in that the markings on terminals Z331 to Z715 are formed back over that portion of the path seeking network f71-g71 simulating the links between penultimate and final switching stages of exchange 71 before a coincidence between markings is sought. A further embodiment is adumbrated in which the availability and location of internal links and other necessary equipment, and the availability of inter-exchange trunks is stored as digital data which is manipulated to determine an entire route from calling subscriber to distant exchange. There is no description in any of the embodiments which explains how the exchange 71 obtains information relating to the availability of trunks between distant exchanges which may be required for the alternate routes.